Starting from a study of phages of Streptococcus pneumoniae (pneumococcus), this work has progressed to plasmids and a novel class of genetic elements that are inserted in the chromosomes of drug-resistant clinical pneumococci and other groups of streptococci. The latter may turn out to be transposons or inserted "pseudoplasmids", but this remains to be established. Their most significant property is that, in the absence of plasmids, these insertions transfer by a conjugation-like process to the chromosomes of other pneumococci. Interspecies transfers are also seen both to and from pneumococci and other streptococcal species. Much of the spread of drug resistance among streptococci appears to be due to this process. Conjugative transfer of chromosomal genes was previously unknown in gram positive eubacteria, and this phenomenon is novel for that reason alone. However, it also appears to differ from conjugation as studied in gram negative bacteria, although there is evidence that this new process may occur in some gram negatives also. We are examining drug resistant pneumococci and some other streptococci to define the structure and functions of the conjugative elements, the molecular nature of the transfer process, and the generality of the phenomenon. Genetic, physical, and molecular mapping methods will be used. For background information and as tools for the above work, phages and plasmids are also being examined. Transformation analysis of the RNA is a central tool for this work.